Electrical actuators that rely on the piezoelectric effect to produce movement in response to applied voltages are known and have found use in many different fields, including electrical switches and positioning devices. In U.S. Pat. No. 3,035,126, granted May 15, 1962 to J. W. Crownover, entitled Transducer, a piezoelectric transducer is described containing a piezoelectric formed in the shape of a hollow cylinder with the electrodes being formed as helical strips that wind about the axis of the cylinder. That transducer produces a twisting motion in response to application of a voltage to the electrodes as enables it to function as an actuator element of an electrical relay device. Conversly, when mechanically twisted the piezoelectric produces a voltage output on the electrodes generally in proportion to the amount of twist and is used as a phonograph needle cartridge.
It is appreciated that the amount of torque required for the relay application of Crownover patent is small. Such prior piezoelectric actuators are not known to be used to directly control aircraft wing flap position or, particularly, helicopter rotor blades, where significant torque is required to pivot an airfoil surface or the like and maintain the surface in the pivoted position. As an advantage, the present piezoelectric actuator may be used in aircraft air foil surface control. The piezoelectric actuator of the invention permits control of a helicopter rotor blade pitch and may be carried on and/or rotated with the helicopter's rotor blade.
Accordingly, an object of the invention is to provide a piezoelectric actuator capable of producing large torque.
An additional object of the invention is to provide a novel electrically operated rotary actuator of novel construction that produces a rotational movement responsive to application of electrical voltage.
A further object of the invention is to provide a new and effective piezoelectric type actuator of simple construction, that may be rotated with and control the pitch of a helicopter rotor blade.
In rotary wing aircraft the conventional means for controlling the craft is by means of a mechanical pushrod bellcrank system that transmits the pilot's inputs to pitch angle of the main rotor blades. For all except the very smallest helicopters, a hydralic boost system is incorporated to aid the pilot. An integral part of the control system is a swashplate that conducts the control motions across the interface between the non-rotating fuselage and the rotating rotor. The swashplate rises and falls in response to the pilot's collective pitch stick to vary the total lift produced by the rotor and tilts as directed by the cyclic pitch stick to vary the pitch angle cyclically around the azimuth for contolling the helicopter's pitch and roll angles and, thereby, the helicopter's direction of flight.
Electrical "fly by wire" controls have heretofore been developed for fixed wing aircraft, both in military and commercial aircraft, to operate the flight control surfaces. In such systems, the control signals are transmitted along wires, eliminating the mechanical pushrods, bellcranks, and cables. The fly-by-wire, and the equivalent fly-by-light systems that transmits control signals by fiber optic means, affords considerable weight savings, especially for larger aircraft.
To date, such fly by wire technology has not been applied to rotorcraft, such as helicopters, because there has been no appropriate replication of the swashplate. Suitable power actuated devices, suitable for a fly by wire system for helicopter control, as could vary the blade pitch angles, until the present invention, were not available.
U.S. Pat. No. 4,519,743, granted May 28, 1985 to N. D. Ham, entitled Helicopter Individual Blade Control System describes a system for controlling the pitch angle of individual helicopter main rotor blades in which an accelerometer carried by the rotor blade provides sensor inputs to control circuits and an electrical servomotor drives the pitch change motions. Although providing additional electronic control, the Ham system, however, continues with the mechanical swashplate and is not a fly-by-wire system.
As an advantage, the present invention eliminates the complicated mechanical swashplate mechanism and replicates its function with a fly-by-wire control that allows simple slip rings to conduct control signals from an electronic controller across the fuselage rotor interface. Effectively the invention provides an electronic swashplate for helicopters.
A further object of the present invention, therefore, is to enable fly by wire control of helicopters.
An additional object of the invention is to provide a non-mechanical swashplate for controlling rotor blade pitch.
And a still additional object of the invention is to provide a helicopter rotor blade whose pitch may be directly controlled by an electrical actuator that is an integral part of the rotor blade assembly.